Photonic milling using dynamic beam arrays

ABSTRACT

A laser processing system includes a beam positioning system to align beam delivery coordinates relative to a workpiece. The beam positioning system generates position data corresponding to the alignment. The system also includes a pulsed laser source and a beamlet generation module to receive a laser pulse from the pulsed laser source. The beamlet generation module generates a beamlet array from the laser pulse. The beamlet array includes a plurality of beamlet pulses. The system further includes a beamlet modulator to selectively modulate the amplitude of each beamlet pulse in the beamlet array, and beamlet delivery optics to focus the modulated beamlet array onto one or more targets at locations on the workpiece corresponding to the position data.

RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/060,199, titled “PHOTONIC CLOCK STABILIZED LASER COMBPROCESSING,” filed Mar. 31, 2008, which is hereby incorporated byreference herein in its entirety.

TECHNICAL FIELD

This disclosure relates to laser processing systems. In particular, thisdisclosure relates to systems and methods for synchronizing selection ofpulses for amplification and alignment with workpiece targets based on aphotonic clock and position data.

BACKGROUND INFORMATION

Lasers may be used in a variety of industrial operations includinginspecting, processing, and micro-machining substrates, such aselectronic materials. For example, to repair a dynamic random accessmemory (“DRAM”), a first laser pulse is used to remove an electricallyconductive link to a faulty memory cell of a DRAM device, and then asecond laser pulse is used to remove a resistive link to a redundantmemory cell to replace the faulty memory cell. Because faulty memorycells needing link removals may be randomly located, workpiecepositioning delay times typically require that such laser repairprocesses be performed over a wide range of interpulse times, ratherthan at a single interpulse time.

Banks of links to be removed are typically arranged on the wafer in astraight row. The links are generally processed in a link run. During alink run, the laser beam is pulsed as a stage positioner passes the rowof links across the location of a focused laser spot. The stagetypically moves along a single axis at a time and does not stop at eachlink position. This production technique is referred to in the industryas on-the-fly (“OTF”) link processing and allows for greater efficiencyin the rate at which links on a given wafer can be repaired, therebyimproving the efficiency of the entire DRAM production process.

As laser pulse repetition frequencies (PRFs) and link run velocitiesincrease, more demands are placed on the stage positioner. Stageacceleration and velocity are not increasing as fast as laser PRFs.Thus, it may be difficult to take the most advantage of forthcoming highPRF lasers (e.g., PRFs in the hundreds of kHz or MHz ranges).

Generally, the current true utilization of laser pulses in a linkprocessing system is quite low. For example, a typical wafer includingapproximately 600,000 links may be processed in approximately 600seconds. This represents an effective blow rate of 1 kHz. If thisexample wafer processing system uses a laser source with a 100 kHz PRF,only about one out of every hundred possible laser pulses reaches thesurface of the wafer.

Dual-beam and multi-beam laser systems generally use complex laseroptical subassemblies and are generally expensive to construct. Further,recent advances in laser design present problems with this approach. Forexample, certain high power, short pulse-width (e.g., on the order ofpicoseconds or femtoseconds) lasers are based on a masteroscillator-power amplifier (MOPA) approach in which a mode-locked laseroscillator provides stable seed pulses at repetition rates in a rangebetween approximately 10 MHz and approximately 100 MHz. These laseroscillators may be actively or passively mode-locked. An actively lockedoscillator may permit some adjustment of its output pulse phase and/orfrequency for timing purposes. However, in a passively mode-lockedmaster oscillator, the output frequency may not be so easily modified.Thus, the laser processing system synchronizes its operation with thefundamental frequency provided by the passively mode-locked masteroscillator.

A power amplifier (e.g., a diode-pumped optical gain medium) amplifiesselected pulses from the master oscillator. As in typical diode-pumpedQ-switched lasers, the energy of these amplified pulses is a function ofthe interpulse period. The true operating repetition rate (e.g., thefrequency of pulses issued from the power amplifier) is typically asub-multiple of the fundamental (e.g., master oscillator) repetitionrate, and is typically about 10 to 1000 times lower than the masteroscillator frequency.

For desired laser operation, the laser should fire at a constantrepetition rate, with the beam positioning subsystem slaved to thelaser's pulse timing. However, achieving such beam position timing whilemaintaining pulse placement accuracy may be quite difficult. Forexample, the timing window for the repetition rates mentioned above maybe in a range between approximately 10 nanoseconds and approximately 100nanoseconds. Servo control systems typically cannot guaranteehigh-accuracy (e.g., within 10 nm) pulse placement within such small,fixed timing windows.

Many industrial laser processing applications (such as link cutting inmemory device redundancy circuits, micro-via drilling, componenttrimming, and material cutting or scribing) emit a high-energy laserpulse in coordination with a motion control system that positions thelaser pulse on a workpiece. This coordination often uses precise timing,and depending on the motion profile of the working beam, this timing maybe arbitrary. While the timing precision is used to maintain theaccuracy of the processing system, the arbitrary timing of pulsecommands can degrade aspects of laser performance, such as pulse widthand peak power.

Many laser processing system designs have incorporated Q-switched lasersto obtain consistent pulse energies at a high pulse repetition rate.However, such lasers may be sensitive to the value of (and variation in)the interpulse period. Thus, pulse width, pulse energy, and pulseamplitude stability may vary with changes in the interpulse period. Suchvariations may be static (e.g., as a function of the interpulse periodimmediately preceding a pulse) and/or dynamic (e.g., as a function ofthe interpulse period history). This sensitivity is generally reduced orminimized by operating the laser processing system such that the laseris fired at a nominal repetition rate (typically below 200 kHz), withminor repetition rate deviations producing acceptable deviations inpulse characteristics.

Such an approach has typically been accomplished by controlling thedesired beam trajectory such that the laser may be fired “on-demand” atthe appropriate workpiece location (or to hit the location with a pulsebased on known factors such as stage velocity, propagation delay, pulsebuild up time, and other delays) to maintain the desired pulse placementaccuracy. The workpiece locations are sequenced such that the repetitionrate is approximately constant. “Dummy” workpiece locations may beinserted in the processing commands to account for laser stabilityissues. The “dummy” workpiece locations keep the repetition rateapproximately constant during idle periods, with the “dummy” pulsesblocked from the workpiece by beam modulation devices such as mechanicalshutters, acousto-optic modulators (AOMs), and electro-optic modulators(EOMs).

SUMMARY OF THE DISCLOSURE

In one embodiment, a laser processing system includes a beam positioningsystem to align beam delivery coordinates relative to a workpiece. Thebeam positioning system generates position data corresponding to thealignment. The system also includes a pulsed laser source and a beamletgeneration module to receive a laser pulse from the pulsed laser source.The beamlet generation module generates a beamlet array from the laserpulse. The beamlet array includes a plurality of beamlet pulses. Thesystem further includes a beamlet modulator to selectively modulate theamplitude of each beamlet pulse in the beamlet array, and beamletdelivery optics to focus the modulated beamlet array onto one or moretargets at locations on the workpiece corresponding to the positiondata.

In certain embodiments, the system also includes a photodetection moduleto sample the beamlet pulses in the beamlet array and to determine atotal energy for each beamlet pulse in the beamlet array. Thephotodetection module is further configured to provide an errorcorrection compensation signal to the beamlet modulator so as to adjustsuccessive beamlet amplitudes provided to a particular target on theworkpiece. The photodetection module may also be configured to determinethat a sum of the pulse energies provided by a series of beamlet pulsesdelivered to a particular target on the workpiece meets or exceeds apredetermined threshold, and control the beamlet modulator to preventfurther beamlet pulses from reaching the particular target.

In certain embodiments, the system further includes a system controlcomputer to cooperate with the beam positioning system to provide thealignment by matching a workpiece target pitch with a pulse repetitionfrequency (PRF) of the pulsed laser source, a beamlet array pitch, and arelative velocity between the beam positioning system and the workpiece(stage velocity).

In another embodiment, a method for processing a workpiece with a laserincludes generating a laser pulse, generating a beamlet array from thelaser pulse that includes a plurality of beamlet pulses, modulating theamplitude of beamlet pulse in the beamlet array, and focusing themodulated beamlet array onto one or more target locations on theworkpiece.

Additional aspects and advantages will be apparent from the followingdetailed description of preferred embodiments, which proceeds withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a conventional laser pulse processingcontrol system including a workpiece (X-Y) positioner.

FIG. 2 is a block diagram of a laser pulse processing system accordingto one embodiment.

FIG. 3 is a flowchart illustrating a method for processing a workpieceusing the system shown in FIG. 2 according to one embodiment.

FIGS. 4A, 4B, 4C, and 4D are flow charts illustrating a few examplemethods for compensating for position errors according to certainembodiments.

FIG. 5 graphically illustrates the use of a vector process combaccording to one embodiment.

FIG. 6 is a block diagram of a photonic milling subsystem for processingworkpiece targets using dynamic beam arrays according to one embodiment.

FIG. 7A is a block diagram of a programmable pulsewidth photonic millingsystem according to one embodiment.

FIG. 7B is a block diagram of the photonic milling subsystem shown inFIG. 7A with a programmable pulsewidth element integrated with a masteroscillator according to one embodiment.

FIGS. 8A, 8B, and 8C schematically illustrate various views of a beamletgeneration module that includes a discretely banded reflectivity plateaccording to one embodiment.

FIG. 9 is a block diagram of a beamlet generation module according toanother embodiment.

FIG. 10 schematically illustrates various patterns typically used forelectrically conductive links.

FIG. 11 is a flow chart of a method for processing a set of targets witha beamlet array according to one embodiment.

FIG. 12 schematically illustrates the relationship between workpiecetarget pitch and beamlet pitch according to one embodiment.

FIG. 13 depicts the processing of a wafer.

FIG. 14 is a schematic diagram of a laser processing system comprisingan AOD according to one embodiment.

FIG. 15 is a schematic diagram illustrating a processing window scanningacross a plurality of laterally spaced link banks according to oneembodiment.

FIG. 16 is a schematic diagram illustrating a processing window scanningacross a plurality of laterally spaced link banks extending along anX-axis and a plurality of link banks extending along a Y-axis accordingto one embodiment.

FIG. 17 is a schematic diagram of a laser processing system comprisingtwo deflection devices according to one embodiment.

FIG. 18 is a schematic diagram of a laser processing system including atelecentric angle detector according to one embodiment.

FIGS. 19A, 19B and 19C are timing diagrams illustrating a series oflaser pulses in relation to respective repositioning profiles accordingto certain embodiments.

FIG. 20 is block diagram of a diffractive optical element configured togenerate an array of beamlets for subsequent modulation and delivery toa workpiece as shown in FIG. 6 according to another embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In one embodiment, a photonic clock is used as a master timing elementto coordinate beam positioner control elements in a laser processingsystem. The photonic clock may be a pulsed output from a photonicoscillator in a pulsed laser source. The photonic oscillator may be aseed oscillator or a master oscillator. The beam positioner controlelements use timing signals from the photonic oscillator to synchronizethe alignment of target structures on a workpiece with the emission oflaser pulses from the laser system. One or more pulses from the lasersource are transmitted through the optical elements of a laser system toprocess the target structures. Pulses from the laser source may beamplitude divided to create arrays of pulses for processing the targetstructures.

The laser systems and methods disclosed herein may be used to process awide variety of workpiece targets. For example, certain embodiments maybe used to sever electrically conductive link structures in a wide arrayof semiconductor memory devices, including DRAM, SRAM, and flash memory;to produce laser drilled micro-vias in flexible circuits, such ascopper/polyamide layered materials, and in integrated circuit (IC)packages; to accomplish laser processing or micromachining ofsemiconductors, such as laser scribing or dicing of semiconductorintegrated circuits, silicon wafers, and solar cells; and to accomplishlaser micromachining of metals, dielectrics, polymeric materials, andplastics. One skilled in the art will recognize that many other types ofworkpieces and/or workpiece structures may be processed according to theembodiments disclosed herein.

Reference is now made to the figures in which like reference numeralsrefer to like elements. In the following description, numerous specificdetails are provided for a thorough understanding of the embodimentsdisclosed herein. However, those skilled in the art will recognize thatthe embodiments can be practiced without one or more of the specificdetails, or with other methods, components, or materials. Further, insome cases, well-known structures, materials, or operations are notshown or described in detail in order to avoid obscuring aspects of theembodiments. Furthermore, the described features, structures, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

I. Typical Synchronization of Triggerable Laser Sources

In a typical laser processing system, timing signals are used to triggera laser source to emit a laser pulse at an appropriate time (e.g., basedon stage velocity, system delays, and other parameters) to illuminate atarget on a workpiece with the laser pulse. For example, FIG. 1 is ablock diagram of a conventional laser pulse processing control system100 including a workpiece (X-Y) positioner 110. A similar system isdescribed in U.S. Pat. No. 6,172,325, by Baird et al., which is assignedto the assignee of the present application. The system 100 includes asystem control computer 112 and an embedded control computer 114 thatinteract to control a beam position controller 116. The beam positioncontroller 116 receives position information from the X-Y positioner110, which positions a workpiece 118 relative to an ultraviolet (UV)laser beam 120. The UV laser beam 120 may propagate through variousoptical elements (not shown) in addition to a fold mirror 122 that isshown. The X-Y positioner 110 may also include a Z positioner 124 thatmay be coupled to either the X or Y stage.

A UV laser system 126 includes a Q-switched solid state infrared (IR)laser 128, such as a diode-pumped, acousto-optically Q-switched Nd:YVO₄laser. The UV laser system 126 also includes an acousto-optic modulator(AOM) 130 for modulating the pulse amplitude of the IR laser 128, and afrequency multiplier 132 for converting the infrared wavelengthemissions from the IR laser 128 into green and/or UV wavelengths byemploying well-known second, third, or fourth harmonic conversionprocesses. The AOM 130 may be alternatively positioned after thefrequency multiplier 132 as indicated by the position of an AOM 134shown in phantom lines. In either embodiment, a laser controller 136controls the transmissivity of the AOM 130 (or the AOM 134) to transmitor block the UV laser beam 120 directed toward the workpiece 118.

The system control computer 112 communicates position coordinates ofprocessing locations on the workpiece 118 across a bus 138 to theembedded control computer 114. In a typical specimen processingapplication, the workpiece 118 includes regularly spaced apart targetsor device structures, such as fusible links, only some of which arelaser processed. The locations processed by the UV laser beam 120 arereferred to as target locations, and the locations that are notprocessed by the UV laser beam 120 are referred to as intermediatelocations. The embedded control computer 114 adds to the target locationcoordinates the intermediate location coordinates that are spaced apartto the IR laser 128 at nearly equal time intervals. The embedded controlcomputer 114 conveys the target and intermediate position coordinatesone at a time at a predetermined rate across a bus 140 to registers 142in the beam position controller 116 and simultaneously loads controldata across a bus 144 to registers 146 in the laser controller 136. Thepredetermined rate controls the movement velocity of the X-Y controller110, and the control data indicate whether the coordinate location is atarget location to be processed and further includes mode and timinginformation.

The laser controller 136 operates timers 148 in either an autopulse modeor a pulse-on-position mode. In the autopulse mode, the timers 148 startin response to the control data in the registers 146. In thepulse-on-position mode, the timers 148 start in response to receiving aposition coincidence signal 150 from a comparator 152 in the beamposition controller 116. Position encoders 154 in the beam positioncontroller 116 indicate to the comparator 152 the current position ofthe X-Y positioner 110, and when the current position matches theposition coordinates stored in the registers 142, the positioncoincidence signal 150 is generated to indicate that the workpiece 118is properly positioned relative to a target position or an intermediateposition. Accordingly, if the workpiece 118 has been positioned relativeto a target position, the timers 148 simultaneously operate the Q-switchin the IR laser 128 (through a Q-switch gating line 158) and set the AOM130 to a transmissive state until a cycle done interrupt 156 is conveyedfrom the timers 148 to the embedded control computer 114. Thetransmissivity of the AOM 130 is controllable as either a laser pulsegating device or as a pulse amplitude modulator. Thus, the IR laser 128may be triggered “on-demand” to process desired targets on the workpiece118.

II. Example System Using Photonic Clock Synchronization

Photonic oscillators may be used in ultrafast laser systems to emitpulses in a nominally fixed frequency comb. Unlike the system 100discussed above, however, photonic oscillators are not directlytriggerable to produce pulses “on-demand.” Rather, the photonicoscillators provide pulses at discrete time intervals at a knownphotonic oscillator frequency f_(osc). Thus, in certain embodimentsdisclosed herein, a laser control system uses a clock derived from thelight pulse output emitted by the photonic oscillator at a first PRF,f_(osc). The laser control system uses workpiece position data andtiming information from the photonic oscillator clock to select pulsesfrom the frequency comb for amplification to a produce process frequencyf_(p) at a second PRF; to further select pulses emitted at the processfrequency f_(p) to transmit towards selected workpiece targets; and tocontrol a beam positioning system and/or cooperating beam positioningcompensation elements to direct the selected pulses to workpiecetargets.

FIG. 2 is a block diagram of a laser pulse processing system 200according to one embodiment. Similar to the system 100 shown in FIG. 1,the system 200 includes an X-Y positioner 110, a system control computer112, an embedded control computer 114, and a beam position controller116. The beam position controller 116 receives position information fromthe X-Y positioner 110, which positions a workpiece 118 relative to alaser beam 210. Although not shown, the laser beam 210 may propagatethrough various optical elements along a laser beam path to a foldmirror 122 that redirects the laser beam 210 toward the workpiece 118.The X-Y positioner 110 may also include a Z positioner 124 that may becoupled to either the X or Y stage.

The system control computer 112 communicates position coordinates ofprocessing locations on the workpiece 118 across a bus 138 with theembedded control computer 114. In one embodiment, the workpiece 118includes regularly spaced apart device structures, such as fusiblelinks, only some of which are laser processed. As discussed above, thelocations processed by the laser beam 210 are referred to as targetlocations, and the locations that are not processed by the laser beam210 are referred to as intermediate locations.

The system 200 also includes a pulsed laser source 212 and a lasersubsystem controller 214 (shown as “LSC”). As shown in FIG. 2, in oneembodiment, the pulsed laser source 212 includes a photonic oscillator216, a first optical modulator 218, and an amplifier 220. The pulsedlaser source 212 may also include a post amplifier 221 and a harmonicconverter module 223. In one embodiment, the photonic oscillator 216 isa mode-locked oscillator as described in U.S. Pat. No. 6,574,250, by Sunet al., which is assigned to the assignee of the current application. Insuch an embodiment, the pulsed laser source 212 is a mode-locked pulsedlaser. Alternatively, the photonic oscillator 216 may be a semiconductorabsorbing mirror passively mode-locked oscillator as taught in U.S. Pat.No. 6,538,298 by Weingarten, et al. Those skilled in the art willappreciate that other oscillators may also be used.

The first optical modulator 218 may be, for example, an acousto-opticmodulator (AOM), an electro-optic modulator (EOM), or other opticalmodulator known in the art. The amplifier 220 and/or the post amplifier221 may include, for example, an optically pumped gain medium. Theharmonic converter module 223 may include nonlinear crystals for theconversion of an incident output pulse to a higher harmonic frequencythrough the well-known method of harmonic conversion.

A photonic clock 222 in the photonic oscillator 216 provides pulsetiming data to the embedded control computer 114 by way of the lasersubsystem controller 214. Using the pulse timing data, the embeddedcontrol computer 114 adds the intermediate location coordinates that arespaced apart to the target location coordinates to create a vectorprocess comb. The vector process comb represents a matrix of target andintermediate target vector coordinates. The embedded control computer114 sends the vector process comb through a bus 140 to registers 142 inthe beam position controller 116. The laser subsystem controller 214 andthe beam position controller 116 use the vector process comb tosynchronize the X-Y positioner 110, in further coordination withcooperating beam position compensation elements described below, withpulses emitted by the pulsed laser source 212.

As discussed in detail below, the photonic oscillator 216 emits a beamof laser pulses at a first PRF, f_(OSC). The first optical modulator 218selects a subset of the pulses from the photonic oscillator 216 to passto the amplifier 220 for amplification and subsequent output by thepulsed laser source 212. The output of the first optical modulator 218is at a second PRF, f_(P). The selection of pulses by the first opticalmodulator 218 is based on a signal from the clock 222 and position datareceived from the beam position controller 116.

The system also includes a second optical modulator 226 used to increasestability of the pulses provided to the workpiece 118. In oneembodiment, timers 148 in the laser subsystem controller 214 control thesecond optical modulator 226 to transmit a pulse from the pulsed lasersource 212 based on timing data. Like the first optical modulator 218,the second optical modulator 226 may be an AOM, an EOM, or another knownoptical modulating device. Although shown external to the pulsed lasersource 212, an artisan will recognize from the disclosure herein thatthe second optical modulator 226 may also be included within the pulsedlaser source 212. In one embodiment, as described in U.S. Pat. No.6,172,325, by Baird et al., which is assigned to the assignee of thepresent application, the second optical modulator 226 is controllable aseither a laser pulse gating device or as a pulse amplitude modulator.Also, as described in U.S. Pat. No. 6,947,454, by Sun et al., which isassigned to the assignee of the present application, the second opticalmodulator 226 may be pulsed at substantially regular and substantiallysimilar repetition rates as that of the pulsed laser source 212.

The system 200 also includes beam position compensation elements todirect the amplified laser pulses to selected targets on the workpiece118. The beam position compensation elements may include anacousto-optic deflector 230, a fast-steering mirror 232, a laser combindexing module 234 discussed below, a combination of the foregoing, orother optical steering elements. One skilled in the art will recognize,for example, that an electro-optic deflector may also be used. Controlof the beam steering elements is based on the photonic clock 222 andposition data received from the beam position controller 116.

III. Example Pulse Synchronization Method

FIG. 3 is a flowchart illustrating a method 300 for processing theworkpiece 118 using the system 200 shown in FIG. 2 according to oneembodiment. After starting 310, the method 300 includes setting 312 thetimers 148 in the laser subsystem controller 214 in a process mode at aPRF determined by the clock 222 in the photonic oscillator 216. Thetimers 148 set pulse block signal 224, 228 to gate the first opticalmodulator 218 and the second optical modulator 226 off, therebypreventing a usable amount of energy emitted by the photonic oscillator216 from reaching the workpiece 118.

When the system 200 prepares to initiate a position-on-pulse processingrun, the embedded control computer 114 receives 314 from the systemcontrol computer 112 target location coordinates on the workpiece 118 tobe processed. As discussed above, the photonic clock 222 in theoscillator module 216 provides the pulse timing data to the embeddedcontrol computer 114. Using the pulse timing data, the embedded controlcomputer 114 computes 316 intermediate location coordinates of targetsnot requiring processing. The embedded control computer 114 adds theintermediate location coordinates to the target location coordinates tocreate a vector process comb. The vector process comb represents amatrix of target and intermediate target vector coordinates.

The embedded control computer 114 sets 316 the system 200 to aposition-on-pulse mode. The embedded control computer 114 also loads 318the vector process comb, representing the location coordinates through abus 140 to registers 142 in the beam position controller 116 and selectsa current location coordinate. Further, the embedded control computer114 communicates position-on-pulse mode enabling data across a bus 144to the laser subsystem controller 214. The timers 148 continue to setthe pulse block signals 224, 228 to cause the first optical modulator218 to block pulsed laser source 212 from transmitting pulse energy tothe workpiece 118. The method 300 then moves 322 the beam positioner 110in response to the current location coordinate.

The method 300 then queries 324 whether a measured position of the X-Ypositioner matches, within accuracy limits, the expected positiondefined by the current location coordinate. Beam position encoders 154in the beam position controller 116 indicate to the comparator 154 thecurrent position of the X-Y positioner 110. The comparator 154 comparesthe data from the beam position encoders 154 to the current locationcoordinate stored in the registers 142. If the data and coordinate matchwithin the predetermined limits, the comparator 154 activates a positioncoincidence signal 150.

If, however, the data and coordinate do not match within thepredetermined limits, the comparator 154 asserts 326 a correctiontrigger signal (not shown). The method then compensates 328 for theposition error. As discussed in detail below, this may be done byadjusting the beam positioning system (e.g., the X-Y positioner 110)and/or cooperating beam positioning compensating elements (e.g., the AOD230 and/or the FSM 232), activating laser comb indexing, implementing arepetitive control algorithm through a resonator stage, a combination ofone or more of the foregoing, and/or by other methods disclosed herein.

When the data and coordinate match within the predetermined limit, themethod 300 starts 330 the timers 148. In one embodiment, the timers 148set 332 the second optical modulator 226 to a transmissive state byapplying a control signal that is substantially coincident with theoutput from the pulsed laser source 212 such that the second opticalmodulator 226 allows the pulse to be transmitted to the workpiece 118.The second optical modulator 226 remains in the transmissive state untilan end 334 of cycle is reached, at which time the timers 148 again set336 the second optical modulator 226 to a reduced transmissive state. Inanother embodiment, the second optical modulator 226 remains in atransmissive state for a pre-determined time sufficient to allowtransmission of the pulse. At the conclusion of this pre-determinedtime, the second optical modulator 226 returns to a reduced transmissivestate. In either embodiment, after the second optical modulator 226 isin the reduced transmissive state, the method 300 returns to step 318 tocontinue with a next current coordinate position.

As discussed above, the first optical modulator 218 selects pulses to beamplified and provided to the second optical modulator at a PRF, f_(P).As taught by Sun et al. in U.S. Pat. No. 6,947,454, which is assigned tothe assignee of the present application, this technique results in athermal loading of the second optical modulator 226 that remainssubstantially constant regardless of the incidence of working pulserequests. This resultant consistent loading on the second opticalmodulator 226 reduces or eliminates deterioration of the laser beamquality and laser beam pointing error associated with thermal loadingvariation. Variations in the pulse to pulse amplitude or the pulse topulse energy may be sensed by a photodetection module (not shown) anddynamic or predictive corrections to a transmission level of the secondoptical modulator 226 may subsequently be controlled to reduce suchpulse to pulse variations.

IV. Example Position Compensation Methods

As discussed above, the method 300 shown in FIG. 3 includes compensating328 for position errors when a current position of the X-Y positioner110 exceeds an expected position window. This may be accomplished in anumber of different ways. FIGS. 4A, 4B, 4C, and 4D are flow chartsillustrating a few example methods for compensating 328 for positionerrors after detecting 410 a correction trigger signal according tocertain embodiments.

In FIG. 4A, the method 328 includes providing 412 the positioncompensation signal to a high-speed beam positioning element, such asthe AOD 230 shown in FIG. 2, so as to adjust the position of the beam210 with respect to the workpiece 118 on the X-Y positioner 110. Asindicated above, an EOD may also be used. The position compensationsignal may include a value indicating a direction and an amount ofdeflection that the AOD 230 is to provide. Such values may be providedby the comparator 154 and/or the position encoders 154 (e.g., throughthe laser subsystem controller 214), which determine the differencesbetween the current position of the X-Y positioner 110 measured by theposition encoders 154 and an expected position stored in the registers142.

The method 328 may query 414 whether the adjustment provided by the AOD230 is sufficient to compensate for the position error, and continue toupdate 416 the position compensation signal until the position of thebeam 210 with respect to the workpiece 118 is within the predeterminedlimits. For example, although not shown in FIG. 2, the position of thelaser beam 210 may be detected by a photodetection module that providesposition correction feedback to the AOD 230.

In FIG. 4B, the method 328 includes providing 412 the positioncompensation signal to the FSM 232 shown in FIG. 2, so as to adjust theposition of the beam 210 with respect to the workpiece 118 on the X-Ypositioner 110. As with the embodiment shown in FIG. 4A, the positioncompensation signal may include a value indicating a direction andamount of deflection that the FSM 232 is to provide. Further, the method328 may query 414 whether the adjustment provided by the FSM 232 issufficient to compensate for the position error, and continue to update416 the position compensation signal until the position of the beam 210with respect to the workpiece 118 is within the predetermined limits.

FIG. 4C is a combination of FIGS. 4A and 4B, wherein the method 328includes providing 420 a primary position compensation signal to the AOD230 and providing 422 a secondary position compensation signal to theFSM 232. Again, the method 328 may query 414 whether the adjustmentprovided by the AOD 230 and/or the FSM 232 is sufficient to compensatefor the position error. The method 300 may update 416 one or both of theprimary position compensation signal and the secondary positioncompensation signal until the position of the beam 210 with respect tothe workpiece 118 is within the predetermined limits. In one embodiment,the method 329 first updates the primary position compensation signal,determines whether the additional adjustment is sufficient, and if not,also updates the secondary position compensation signal. This sequencemay be repeated until the position of the beam 210 with respect to theworkpiece 118 is within the predetermined limits.

In FIG. 4D, the method 328 includes providing 424 the positioncompensation signal to the laser comb indexing module 234. The lasercomb indexing module 234 changes 426 a laser comb index k in the vectorprocess comb based on a desired amount of compensation (e.g., the amountindicated by the position compensation signal). The laser pulse index kis an integer value used to determine which pulses from the photonicoscillator 216 to transmit from the pulsed laser source 212 using thefirst optical modulator 218. As discussed below with reference to FIG.5, the laser comb index k is applied by incrementing or decrementing asecond frequency comb (f_(P)) to produce an offset frequency comb(f_(P)′). In the example shown, the laser comb indexing module 234commands the laser comb index k to an offset of 1 (k=1) followingselection by the first optical modulator 218 photonic oscillator pulsenumber m=1, thereby resulting in subsequent amplification of thephotonic oscillator pulse number m=12 in offset process frequency combf_(P)′.

FIG. 5 graphically illustrates the use of a vector process combaccording to one embodiment. As shown the photonic oscillator 216provides a series of pulses 510 at a first PRF f_(OSC). The time betweensuccessive pulses 510 (interpulse period) may be on the order ofapproximately 1 nanosecond to approximately 100 nanoseconds. Interpulseperiods greater than approximately 100 nanoseconds may also be used.Those skilled in the art will further appreciate that very compactoscillators with interpulse periods of less than approximately 1nanosecond may also be used. At these speeds, it may be difficult orimpossible for the beam positioning system (e.g., the X-Y controller110) to accurately align particular targets on the workpiece 118 withthe laser beam 210. Further, it may be difficult or impossible for theamplifier 220 to efficiently amplify each pulse provided by the photonicoscillator 216. Thus, the first optical modulator 218 operates at asecond PRF f_(P) to select every n^(th) pulse for transmitting to theworkpiece 118. The second PRF f_(P)=f_(OSC)/n. In the example shown inFIG. 5, the process frequency index n=10 such that transmitted pulses(e.g., when there is no position compensation by incrementing the lasercomb index k) correspond to oscillator frequency comb pulses m=11, m=21,m=31, and so forth. An artisan will recognize from the disclosure hereinthat any other integer value may also be used for the process frequencyindex n. The process frequency index n may be chosen, for example, suchthat the X-Y positioner 110 is capable of moving between targets at thesecond PRF f_(P) while maintaining the positioning error withinpredetermined limits.

As further shown in FIG. 5, the laser comb index k may be incrementedbetween two successive pulses by an integer photonic oscillatorinterpulse interval without modifying of the laser PRF (e.g., f_(P))commanded by the system control computer 112. In this example, the lasercomb index k is incremented from k=0 to k=1 after a first pulse m=1 istransmitted by the first optical modulator 218 for amplification.Because n=10 is unchanged, there are still 10 pulses emitted from thephotonic oscillator 216 between each of the pulses m=12, m=22, m=32,m=42 . . . corresponding to the offset process frequency f_(P)′. Thus,incrementing the laser comb index k after the first pulse m=1 timeshifts the succeeding pulses m=12, m=22, m=32, m=42 . . . transmitted bythe first optical modulator 218 in the process comb by an integer valueof 1/f_(OSC), while the new PRF f_(P)′ at which working pulses areemitted is equal to f_(P).

Referring again to FIG. 4D, the method 328 may also include selectivelyblocking 428 a first pulse m=12 incident on the second optical modulator226 after incrementing the laser comb index k for pulse amplitudestabilization. Using the second optical modulator 226 to block the firstpulse m=12 allows for a settling interval to enable pulse amplitudestabilization following laser comb indexing in which an interpulseperiod was longer (or shorter) than 1/f_(P).

Incrementing the laser comb index k between two successive pulsesresults in a laser beam shift at the work surface=(shift in k)*(beampositioner velocity*(1/f_(OSC))). As an illustrative numerical example,if f_(OSC)=10 MHZ, f_(P)=1 MHz and the beam positioner velocity=500nm/μs, a shift of k=1 (say from pulse m=10 to pulse m=11) results in awork surface shift of (500 nm/μs×0.1 μs)=50 nm. If in the same example,we had used a f_(OSC)=100 MHz, the work surface shift=5 nm. These valuesrepresent a laser comb augmentation capability that may further assistthe beam displacement and other positioning elements to enable workinglaser pulses to intercept assigned workpiece target locations. As thoseskilled in the art will recognize, bursts of pulses at PRF f_(P) may bealternatively employed and laser comb indexed, as commanded by embeddedcontrol computer in coordination with the beam position controller 116.

An artisan will recognize from the disclosure herein that any of theembodiments disclosed herein for position error compensation may becombined to improve speed and accuracy. Further, position errorcompensation is not limited to the embodiments shown in FIGS. 4A, 4B,4C, 4D, and 5. For example, in another embodiment, servo tracking errormay be driven to near-zero through the use of a repetitive controlalgorithm through employment of a resonator stage. In this embodiment,target runs are made at high velocity and high acceleration. The chuckstage repeats precisely the same motion (no gap profiling) so thatiterative learning algorithms can reduce repeatable errors to withinsatisfactory tolerances. Further compensation can then be employed usingbeam compensation elements, as described above.

In addition, or in other embodiments, beam deflection elements (e.g.,the AOD 230 or FSM 232) may steer the beam 210 to correct for velocityerror that is integrated with time. If the velocity is too slow, thenthe system 200 system may skip a laser pulse to stay within thedeflection range of the beam steering device. If the velocity is toohigh, such that the system 200 runs out of range on the deflectiondevice, the system 200 may process certain links on a first run and thenperform a second or additional runs to process other targets. This maynot be desirable because it generally increases processing time. Thus,in some embodiments the system 200 may process a link run slower thanthe product of PRF*target pitch such that worst case velocity neverexceeds PRF*pitch.

In a separate embodiment, single or multiple output pulses from thephotonic oscillator 216 may be directly employed in processes wherephotonic oscillator output energy per pulse is sufficient for efficientphotonic comb laser processing of workpieces.

V. Example Photonic Milling Using a Modulated Beamlet Array

In one embodiment, the systems and methods described herein are used forarray milling of workpiece targets, including semiconductor linkstructures. As discussed below, the laser pulse processing system 200shown in FIG. 2 may include a photonic milling subsystem configured toproduce an array of beamlets from the laser beam 210 generated by thepulsed laser source 212. The photonic subsystem modulates each beamletand provides the modulated array of beamlets to targets on the workpiece118. The system control computer 112 and/or the embedded controlcomputer 114 are configured to determine the number of pulses that maybe employed from the modulated array of beamlets to process a specificworkpiece structure. In addition, or in another embodiment, thepulsewidth of a picosecond MOPA laser source is programmed by varying aspectral bandpass element inserted in the master oscillator. In certainembodiments, the master oscillator is used as a reference timing elementfor the beam positioning system, as discussed above.

As discussed below, the array of beamlets may be generated, for example,using gradient reflectivity plates. The array of beamlets may also begenerated, for example, using polarization splitting and recombinationoptics. The array of beamlets may also be generated using one or morediffractive optical element (see FIG. 20 discussed below).

The photonic milling subsystem may include a variety of different lasersources. In one embodiment, the laser source includes a diode-pumpedpassively mode-locked MOPA configured to produce suitable energy perpulse at PRFs greater than approximately 10 kHz, and more preferablyabove approximately 100 kHz. A tandem photonic amplifier may be usedthat employs a fiber master oscillator, as described by Baird, et. al.in International Application Publication No. WO 2008/014331. In certainsuch embodiments, the fiber master oscillator provides laser pulses withpulse durations in a range between approximately 100 femtoseconds andapproximately 500 picoseconds. In yet another embodiment, a pulsedmaster oscillator fiber power amplifier (MOFPA) may be used.

FIG. 6 is a block diagram of a photonic milling subsystem 600 forprocessing workpiece targets using dynamic beam arrays according to oneembodiment. The photonic milling subsystem 600 includes a laser source610, conditioning optics 612, a beamlet generation module 614, a beamletmodulator 616, a photodetection module 618, and beamlet delivery optics620.

A laser beam 622 from the laser source 610 is directed through the beamconditioning optics 612 to the beamlet generation module 614. Asdiscussed in detail below, the beamlet generation module 614 separatesthe laser beam 622 into a beamlet array 624. For discussion purposes,the beamlet array 624 may be referred to herein as an q×r beamlet array624, where q represents the number of beamlets in a first direction(e.g., row) and r represents the number of beamlets in a seconddimension (e.g., column) in the array. The beamlet generation module 614provides the q×r beamlet array 624 to the beamlet modulator 616, whichattenuates each incident beamlet to a commanded output beamlet energyvalue. The beamlet modulator 616 outputs a modulated q×r beamlet array626 that is sampled by the photodetection module 618 and provided to thebeamlet delivery optics 620. The beamlet delivery optics 620 focus themodulated q×r beamlet array 626 onto the workpiece 118. The energy valueof each beamlet in the modulated q×r beamlet array 626 is commanded, forexample, by the system control computer 112 shown in FIG. 2.

(A) Laser Sources and Modulation Methods for Photonic Milling

In one embodiment, the laser source 610 includes the pulsed laser source212 shown in FIG. 2 and described in detail above.

In another embodiment, the laser source 610 includes a tandem photonicamplifier employing a picosecond fiber master oscillator. In one suchembodiment, the fundamental laser output may subsequently be coupled toa harmonic conversion module (such as the harmonic conversion module 223shown in FIG. 2) to produce harmonic output. The tandem photonicamplifier may incorporate a diode-pumped fiber master oscillatoremitting at a pulsewidth in a range between approximately 500nanoseconds and approximately 1 picoseconds, at a wavelength in a rangebetween approximately 2.2 μm and approximately 100 nm, and morepreferably at a wavelength in a range between approximately 2.0 μm andapproximately 200 nm.

Modulation methods may include direct modulation of a seed diode,external modulation of pulsed or continuous wave (CW) seed output, orexternal modulation of the input to the power amplifier stage by AOMsand/or EOMs. Modulation of the pump power supplied to the poweramplifier stage may also be employed to further modify the temporalpulse shape produced by the laser source 610.

In another embodiment, the laser source 610 includes a q-switcheddiode-pumped solid state laser emitting at a pulsewidth betweenapproximately 500 nanoseconds and approximately 100 picoseconds, at awavelength in a range between approximately 2.2 μm and approximately 150nm. The laser source 610 may use intracavity or extracavity harmonicconversion optics. The laser source 610 may be capable of CW emission.In this case, modulation of the RF window gate supplied to the q-switchprovides control of the temporal pulse shape. Modulation of the diodepump power supplied to the solid state laser may also be employed tofurther modify the temporal pulse shape produced by laser sourcesubsystem.

In another embodiment, the laser source 610 is a MOPA emitting at apulsewidth in a range between approximately 100 picoseconds andapproximately 10 femtoseconds, at a wavelength in a range betweenapproximately 2.2 μm and approximately 150 nm. The laser source 610 mayemploy intracavity or extracavity harmonic conversion optics. Modulationmethods may include diode pump modulation or external modulation of theinput to the power amplifier by AOMs and/or EOMs. Modulation of the pumppower supplied to the power amplifier may also be employed to furthermodify the temporal pulse shape produced by the laser source 610. In oneembodiment, the master oscillator is a fiber laser master oscillator andthe power amplifier is a fiber power amplifier. Those skilled in the artwill recognize this configuration as an ultrafast fiber laser.

In yet another embodiment, the laser source 610 includes a tunablepulsewidth MOPA emitting at a pulsewidth in a range betweenapproximately 100 picoseconds but greater than 10 femtoseconds, at awavelength in a range between approximately 2.2 μm and approximately 150nm. For example, FIG. 7A is a block diagram of a programmable pulsewidthphotonic milling system 700 according to one embodiment. The system 700includes a graphical user interface (GUI) 710 to provide pulsewidthselection through a system control computer 112, subsystem controlelectronics 712, and a photonic milling subsystem 600′ that includes alaser source 610′ with a programmable pulsewidth element 714. A user mayuse the pulsewidth selection GUI 710 to selectively change thepulsewidth of the laser beam 622 generated by the laser source 610′. Inresponse to the user's selection, the subsystem control electronics 712controls the programmable pulsewidth element 714 to adjust thepulsewidth.

In one such embodiment, the programmable pulsewidth element 714 isinserted into the master oscillator to allow discrete pulsewidthtunability of the laser source 610′ in a range between approximately 50picoseconds and approximately 10 femtosecond. For example, FIG. 7B is ablock diagram of the photonic milling subsystem 600′ shown in FIG. 7Awith a programmable pulsewidth element 714 integrated with a masteroscillator 716 of a MOPA 718 according to one embodiment. The MOPA 718includes a power amplifier 720. In the example embodiment shown in FIG.7B, the programmable pulsewidth element 714 includes a programmablebandpass filter.

The laser source 610′ with the programmable pulsewidth element 714 mayemploy intracavity or extracavity harmonic conversion optics. Modulationmethods may include diode pump modulation or external modulation of theinput to the power amplifier 720 by AOMs and/or EOMs. Modulation of thepump power supplied to the power amplifier 720 may also be employed tofurther modify the temporal pulse shape produced by the laser source610′. In one embodiment, the master oscillator 716 is a fiber lasermaster oscillator and the power amplifier 720 is a fiber poweramplifier.

Returning to FIG. 6, in another embodiment, the laser source 610includes a master oscillator regenerative amplifier emitting at apulsewidth in a range between approximately 50 picoseconds andapproximately 10 femtoseconds, at a wavelength between approximately 2.2μm and approximately 150 nm. The laser source 610 may employ intracavityor extracavity harmonic conversion optics. Modulation methods mayinclude diode pump modulation or external modulation of the input to thepower amplifier by AOMs and/or EOMs. Modulation of the pump powersupplied to the power amplifier may also be employed to further modifythe temporal pulse shape produced by laser subsystem.

(B) Beamlet Generation

FIGS. 8A, 8B, and 8C schematically illustrate various views of a beamletgeneration module 614 that includes a discretely banded reflectivityplate 810 according to one embodiment. FIG. 8A schematically illustratesa side view of the discretely banded reflectivity plate 810, whichincludes a first surface S1 and a second surface S2. FIG. 8Bschematically illustrates a front view of the first surface S1. FIG. 8Cschematically illustrates a front view of the second surface S2. Asshown in FIGS. 8A and 8B, the first surface S1 and the second surface S2include discrete portions or bands that each has a respectivereflectivity R1, R2, . . . , Rn.

As shown in FIG. 8A, the bands are arranged on the first surface S1 andthe second surface S2 such that an input laser beam 622 (e.g., providedby the laser source 610) enters the discretely banded reflectivity plate810 through the first surface S1, is partially reflected from andpartially transmitted through the second surface S2 to form a firstbeamlet 812. The first surface S1 reflects the portion of the beam thatdid not form part of the first beamlet 812 back toward the secondsurface S2. The second surface S2 again partially reflects the beam andpartially transmits the beam to form a second beamlet 814. The firstsurface S1 reflects the portion that did not form part of the secondbeamlet 814 back toward the second surface S2. The second surface S2again partially reflects the beam and partially transmits the beam toform a third beamlet 816. This process repeats until the discretelybanded reflectivity plate 810 produces a desired number of beamlets forthe beamlet array 624. Although not shown, the beamlet generation module614 may include one or more beamsplitters to direct portions of theinput laser beam 622 to multiple discretely banded reflectivity plate's810 to produce a q×r beamlet array 624.

FIG. 9 is a block diagram of a beamlet generation module 614 accordingto another embodiment. The beamlet generation module 614 of this exampleembodiment includes a first quarter wave plate 910, a polarizingbeamsplitter cube 912, a second quarter wave plate 914, a first mirror916, a third quarter wave plate 918, and a second mirror 920. The firstquarter wave plate 910 receives an incident linearly polarized laserbeam 622 and transmits a circularly polarized beam into the polarizingbeamsplitter cube 912. A fraction of the circularly polarized beam istransmitted through an output surface of the polarizing beamsplittercube 912 as a first beamlet 922. Another fraction of the circularlypolarized beam is then reflected into a first channel of the polarizingbeamsplitter cube 912 where it is directed through the second quarterwave plate 914 to the first mirror 916. The beam reflects off the firstmirror 916 and makes a second pass through the second quarter wave plate914 to become p-polarized. The p-polarized component enters a secondchannel of the polarizing beamsplitter cube 912, where after similartransmission through the third quarter wave plate 918, reflection offthe second mirror 920, and transmission a second time through the thirdquarter wave plate 918, it is emitted through the output surface of thepolarizing beamsplitter cube 912 as a second beamlet 924. Additionalbeamlet array generating modules 614, such as that shown in FIG. 9, maybe employed to produce additional beamlets in a q×r beamlet array 624.In addition, or in another embodiment, one or more diffractive opticalelement 2010 may generate beamlets in a q×r beamlet array 624, as shownin FIG. 20. The diffractive optical element 2010 may include a gratingshaped to generate a desired distribution of beamlets in atwo-dimensional or three-dimensional array 624.

Returning to FIG. 9, the first beamlet 922 and the second beamlet 924may be approximately collinear or may be randomly offset from oneanother due to variations in the alignment of the optical components ofthe beamlet array generating module 614. An artisan will recognize fromthe disclosure herein, however, that a controlled amount of offset maybe introduced into the optics of the beamlet array generating module 614such that the paths of the first beamlet 922 and the second beamlet 924are substantially parallel to, and at a desired distance from, oneanother. For example, the second mirror 920 shown in FIG. 9 may bereplaced by a pair of mirrors (not shown) whose vertex of intersectionlies along a line parallel to the midpoint of the polarizingbeamsplitter cube 912. As another example, the offset may be provided byslightly tilting the mirrors 916, 920 in a complementary fashion (e.g.,rotate one clockwise and the other counter-clockwise). Those skilled inthe art will recognize other ways to offset the paths of the firstbeamlet 922 and the second beamlet 924.

(C) Target Alignment

In one embodiment, the system control computer 112 controls the X-Ypositioner 110 shown in FIG. 2 to coordinate delivery of the modulatedq×r beamlet array 626, which is focused by the beamlet delivery optics620 to specific targets on the workpiece 118. In one embodiment, acurrent position signal is generated for each addressable beamlet.Discrete or multi-channel beam position compensation elements may beemployed in combination with laser comb indexing, as discussed above, toachieve current position performance within predetermined accuracylimits.

The workpiece targets may include, for example, electrically conductivelinks arranged on a semiconductor device. As discussed above, laserpulses may be used to remove electrically conductive links to faultymemory cells of a DRAM device. Such electrically conductive links may bearranged in one-dimensional or two-dimensional patterns. For example,FIG. 10 schematically illustrates various patterns typically used forelectrically conductive links 1010. The shown patterns include a ladderpattern 1012, a fork pattern 1014, a fishbone pattern 1016, and astaggered pattern 1018. An artisan will recognize from the disclosureherein, however, that any pattern may be used.

In one embodiment, the system control computer 112 operates the X-Ypositioner 110 in a step and repeat pattern so as to spatially match thefocused modulated q×r beamlet array 626 to workpiece targets. Forexample, FIG. 11 is a flow chart of a method 1100 for processing a setof targets (such as the electrically conductive links 1010 shown in FIG.10) with a beamlet array 624 according to one embodiment. After starting1110, the method 1100 includes aligning 1112 a plurality of beamletpaths with respect to the set of targets. For example, the systemcontrol computer 112 may control the X-Y positioner 110 and the beamletdelivery optics 620 so as to spatially align q×r beamlet paths with q×rtargets arranged in a pattern on the workpiece 118.

After aligning the beamlet paths with the targets, the laser source 610generates 1112 a laser pulse 622, the beamlet generation module 614divides 1116 the laser pulse into a beamlet array 624, the beamletmodulator 616 modulates 1118 the beamlet array 624, and the beamletdelivery optics 620 focus 1120 the modulated beamlet array 626. Themethod 1100 then processes 1122 the set of targets with the focusedmodulated beamlet array 626, and queries 1124 whether there is anotherset of targets to process. If there is another set of targets toprocess, the system control computer 112 aligns 1112 the beamlet pathswith the new set of targets and repeats the method 1100. Once all setsof targets have been processed, the method 1100 ends 1126.

In another embodiment, the system 200 control computer 112 matches theworkpiece target pitch to the laser PRF, the beamlet array pitch, andthe velocity of the X-Y beam positioner 110 such that a workpiece targetis sequentially processed by a sum of single pulses delivered bymultiple beamlets. FIG. 12 schematically illustrates the relationshipbetween workpiece target pitch 1208 and beamlet pitch 1210 according toone embodiment. As shown, the distance or pitch between beamlets 1212(beamlet pitch 1210) is related to the pitch between targets 1214(target pitch 1208) and the PRF of the laser source 610 through therelationship:

c×(beamlet pitch)=d×(workpiece target pitch),

where c and d are integers, where:

workpiece target pitch=stage velocity/PRF,

and where preferably the integers c and d are selected such that:

c/d=an integer value.

In FIG. 12, the beamlet pitch 1210 is represented by (Δx_(BL))^(i,j) andthe workpiece pitch 1208 is represented by (Δx_(p))^(h), where i is thebeamlet number index, j is the pulse number index, and h is theworkpiece target index. Thus, for example, a particular beamlet igenerated from a particular pulse j may be represented herein as(bi:pj). The maximum deliverable pulse number per workpiece target whenthe stage is traveling at a constant velocity (in the absence ofsequential scans) is equal to the number of beamlets, i. As a practicalexample, consider the case of three beamlets 1212 (i=3) generated fromeach successive laser pulse j. In this example, a laser beam path movesfrom left to right over the workpiece targets 1214 shown in FIG. 12 assuccessive laser pulses are emitted from a laser source. A firstworkpiece target 1214 is sequentially processed by a third beamlet 1212generated from a first pulse (b3:p1), a second beamlet generated fromthe first pulse (b2:p1), and a first beamlet generated from the firstpulse (b1:p1). A second target 1214 is processed by a third beamlet of asecond pulse (b3:p2); a second beamlet of the second pulse (b2:p2); anda first beamlet of the second pulse (b1:p2).

(D) Beamlet Amplitude Control

In one embodiment, the focused modulated beamlet array 626 is amplitudeaddressable. The amplitude of each beamlet 1212 in the array 626 isdenoted as b_(j):p_(i):A, where A is a real number between 0 and 1,where 0 indicates minimum pulse amplitude, where 1 indicates maximumpulse amplitude, and wherein intermediate values represent scaledamplitude values between these minimum and maximum values. As apractical example, again taking the case of three beamlets (i=3), if thefirst target 1214 and the third target 1214 are milled a maximum pulsenumber and a maximum amplitude per pulse, and if the second target 1214is not milled, then the photonic milling pattern is programmed as:

First workpiece target: (b3:p1:1); (b2:p1:1); (b:p1:1),

Second workpiece target: (b3:p2:0); (b2:p2:0); (b1:p2:0),

Third workpiece target: (b3:p3:1); (b2:p3:1); (b1:p3:1).

In one embodiment, the photodetection module 618 shown in FIG. 6 isconfigured to calculate, in real-time, the total energy applied perbeamlet 1212 to a particular workpiece target 1214. The photodetectionmodule 618 provides an error correction compensation signal to thebeamlet modulator 616 to adjust successive beamlet amplitudesb_(j):p_(i):A_(i,j,h). This allows for very fine control of the totalenergy per pulse delivered to the workpiece targets 1214. It also allowsfor precise control of total energy applied to a particular target 1214.For example, the photodetection module 618 may determine that the totalenergy of a series of beamlets 1212 applied to a particular target 1214meets or exceeds a predetermined threshold value. Once the threshold ismet, the photodetection module 618 may control the beamlet modulator 616to block additional beamlets 1212 from being transmitted to thatparticular target 1214. An artisan will recognize from the disclosureherein that other elements may also be used to control the energy perpulse, or the total energy applied to a particular target 1214. Forexample, the photodetection module 618 may provide feedback to theprogrammable pulsewidth element shown in FIGS. 7A and 7B to adjust theenergy of the pulses provided by the laser source 610′.

VI. Example Swath Processing

The systems and methods described herein may be used in a swathprocessing embodiment wherein pulses may be deflect along a row, oramong adjacent rows, of target structures on a workpiece on-the-fly. Asdiscussed above, the photonic oscillator 216 shown in FIG. 2 providespulses at a high PRF (e.g., from tens of kHz to a few MHz) that may bedirected by beam positioning elements (e.g., the AOD 230, the FSM 232,and/or the laser comb indexing module 234) in a moving processingwindow.

By way of example, FIG. 13 depicts the processing of a wafer 1310. Aconventional sequential link blowing process requires scanning the X-Ymotion stage 110 across the wafer 1310 once for each link run.Repeatedly scanning back and forth across the wafer 1310 results incomplete wafer processing. A machine typically scans back and forthprocessing all X-axis link runs 1312 (shown with solid lines) beforeprocessing the Y-axis link runs 1314 (shown in dashed lines). Thisexample is merely illustrative. Other configurations of link runs andprocessing modalities are possible. For example, it is possible toprocess links by moving the wafer or optics rail. In addition, linkbanks and link runs may not be processed with continuous motion.

For a wafer 1310 comprising DRAM, for example, memory cells (not shown)may be located in the areas 1316 between the X-axis link runs 1312 andthe Y-axis link runs 1314. For illustrative purposes, a portion of thewafer 1310 near an intersection of an X-axis link run 1312 and a Y-axislink run 1314 is magnified to illustrate a plurality of links 1318arranged in groups or link banks. Generally, the link banks are near thecenter of a die, near decoder circuitry, and not above any of the arrayof memory cells. The links 1318 cover a relatively small area of thetotal wafer 1310.

FIGS. 14, 17, and 18 provide example alternative embodiments for swathprocessing and are provided for illustrative purposes. One skilled inthe art will recognize that the principles of swath processing discussedin relation to FIGS. 14, 17, and 18 may be applied to the otherembodiments (e.g., FIG. 2) discussed herein.

FIG. 14 is a schematic diagram of a laser processing system 1400comprising an AOD 1410 according to one embodiment. The AOD 1410comprises a very high speed device configured to deflect a pulsed laserbeam 1412 emitted by a laser 1414 such that two sequential pulses may bedelivered to two different links in two laterally spaced link banks. Inone embodiment, the AOD 1410 is configured to deflect laser pulses inone dimension (e.g., perpendicular to a scanning direction). In anotherembodiment, the AOD 1410 is configured to deflect laser pulses in twodimensions (e.g., perpendicular to a scanning direction and parallel tothe scanning direction). In other embodiments, two AODs are used toprovide deflection in a two dimensions.

In one embodiment, the laser processing system 1400 also includes aswitch 1416 configured to allow or block laser pulses from reaching aworkpiece 1418 (e.g., a semiconductor wafer including a plurality oflinks). The switch 1416 may include an AOD or acousto-optic modulator(AOM) device. In one embodiment, however, the switch 1416 and the AOD1410 comprise a single device configured to selectively direct thepulsed laser beam 1412 to a beam dump (not shown) to block laser pulsesfrom reaching the workpiece 1418.

As also shown in FIG. 14, the laser processing system 1400 may alsoinclude a relay lens 1422 to direct differently deflected beam paths(illustrated exiting the AOD 1410 as a solid line and a dashed line) toa same location on a mirror 1424 (or other redirection device such as anFSM) corresponding to an entrance pupil of a focus lens 1426. Inoperation, different deflection angles provided by the AOD 1410 resultin different pulses being directed to different locations on theworkpiece 1418. Although not shown, in one embodiment, a controllerconfigured to execute instructions stored on a computer readable mediumcontrols the AOD 1410 so as to selectively deflect a sequence of laserpulses to desired locations on the workpiece 1418.

An artisan will recognize from the disclosure herein that the system1400 is provided by way of example and that other system configurationsare possible. Indeed, various other example system embodiments areprovided below.

FIG. 15 is a schematic diagram illustrating a processing window 1500scanning across a plurality of laterally spaced link banks 1510, 1512,1514, 1516, 1518, 1520 according to one embodiment. Each link bank 1510,1512, 1514, 1516, 1518, 1520 includes a plurality of links 1522 that arenot severed and a plurality of links 1524 that are severed by a seriesof laser pulses as the processing window 1500 scans across the pluralityof link banks 1510, 1512, 1514, 1516, 1518, 1520.

In one embodiment, a laser processing system 1400 is configured to severany link 1522, 1524 within the moving processing window 1500. Thus,rather than using six individual link runs to process the six link banks1510, 1512, 1514, 1516, 1518, 1520 included in the example shown in FIG.15, the system 1400 processes all six link banks 1510, 1512, 1514, 1516,1518, 1520 in a single pass, greatly improving system throughput. In oneembodiment, for example, a system including a 100 kHz laser providedthrough a single beam path, a 50 μm×50 μm processing window, and a lowperformance stage (e.g., 1 G accelerations per axis and 20 ms settletimes), may have an increased throughput that is two to three times thatof conventional link processing systems. Such a system would becompetitive with a dual-beam system including a high PRF laser (e.g.,300 kHz) and a high performance stage (e.g., 1 m/second link runs, 5 Gaccelerations, and 0.001 second settle times). It may be significantlyeasier and cheaper to build the system having the lower performancestage. Further, the single beam system may be easier and cheaper tobuild than the dual-beam system.

In one embodiment, the processing window 1500 scans across the pluralityof link banks 1510, 1512, 1514, 1516, 1518, 1520 in a substantiallycontinuous motion as the plurality of links 1524 are severed. In anotherembodiment, the processing window 1500 steps across the plurality oflink banks 1510, 1512, 1514, 1516, 1518, 1520 in a series of discretemovements. In one such embodiment, the processing window comprises twomutually exclusive sets of links 1522, 1524 between each step or hop.Thus, the system 1400 may process a first set of links 1522, 1524 inboth on-axis and cross-axis directions within the processing window 1500at a first location before the processing window 1500 moves to a secondlocation that includes a second (and different) set of links. In anotherembodiment, the processing window 1500 takes smaller steps in the scandirection such that when one group (e.g., one column) of links 1522,1524 corresponding to respective link banks 1510, 1512, 1514, 1516,1518, 1520 enters the scanning window 1500 during a step, another groupof links 1522, 1524 exits the scanning window 1500. Thus, the system1400 processes a group or column of laterally spaced links 1522, 1524 indifferent link banks 1510, 1512, 1514, 1516, 1518, 1520 between eachstep.

An artisan will understand from the disclosure herein that, depending onthe relative sizes of the processing window 1500 and the link banks1510, 1512, 1514, 1516, 1518, 1520, the system 1400 may process morethan six link banks in a single pass. Further, the system 1400 mayprocess less than six link banks in a single pass, including, forexample, processing a single link bank in a single pass.

An artisan will also understand from the disclosure herein that thesystem 1400 is not limited to processing substantially parallel,laterally spaced link banks 1510, 1512, 1514, 1516, 1518, 1520 withinthe processing window 1500. Indeed, the links 1522, 1524 passing throughthe processing window 1500 may be arranged in any pattern. The severedlinks 1524 may also be severed in any sequence. Further, while FIG. 15shows a uniform scan direction in the X-direction (horizontal), the scandirection may also be in the Y-direction (vertical), a combination of Xand Y directions, and/or a random pattern around the XY plane of awafer. In one embodiment, the scan direction is selected so as tooptimize throughput.

For example, FIG. 16 is a schematic diagram illustrating a processingwindow 1500 scanning across a plurality of laterally spaced link banks1510, 1512, 1514, 1516, 1518, 1520 extending along an X-axis and aplurality of link banks 1610, 1612 extending along a Y-axis according toone embodiment. In a single pass of the processing window 1500 over thelaterally spaced link banks 1510, 1512, 1514, 1516, 1518, 1520 extendingalong the X-axis, the processing window 1500 also passes over at least aportion of the links 1522, 1524 in the plurality of link banks 1610,1612 extending along the Y-axis. Again, as shown in FIG. 16, the system1400 may selectively sever any of the links 1522, 1524 passing throughthe processing window 1500.

In one embodiment, the system 1400 sorts and orders the sequence of linkblows within the processing window 1500 so as to maximize or increasethroughput. To achieve this maximized or increased throughput, thesystem 1400 also calculates a stage velocity that is compatible with thesize of the processing window 1500, the number of links 1522, 1524within the processing window 1500 to be blown at any given time, and thesequence of link blows. In one such embodiment, the system 1400 selectsa stage velocity so as to reduce the number of blocked pulses. The stagevelocity may also be selected to ensure that every link intended to beblown is blown in a single pass of the processing window 1500. In oneembodiment, the stage velocity may be constant.

In other embodiments, the stage velocity may vary based on the number oflinks 1524 to be blown currently passing through the processing window1500. For example, when fewer links 1524 to be blown are passing throughthe processing window 1500, the system 1400 may increase the stagevelocity. When more links 1522, 1524 to be blown are passing through theprocessing window 1500, the system 1400 may decrease the stage velocity.

In one embodiment, a maximum stage velocity V_(SMAX) is determined byfinding the maximum number of links (N_(MAX)) within the processingwindow 1500 over a group of link runs. For example, the maximum stagevelocity V_(SMAX) may be set to the width (AOD_(width)) of theprocessing window 1500 multiplied by the PRF divided by N_(MAX). Thisprovides a good estimate for the maximum stage velocity V_(SMAX).However, in one embodiment, the system 1400 takes into account possible“queueing” of the links 1522, 1524 in the processing window 1500, whichprovides a buffer for unprocessed links over short sections of the linkruns when the velocity exceeds the above limit. Depending on the densityof the link runs, such queueing may increase the stage velocity in arange between approximately 50% and approximately 100%. This improvementmay be diluted in some embodiments by acceleration/deceleration timesand overhead. In one embodiment, using queueing to determine the maximumstage velocity V_(SMAX) is an iterative process wherein an overflow of a“link queue” becomes very non-linear as a true maximum velocity isapproached. In such embodiments, more linearity may be introduced by,for example, filtering the link density, calculating a “link flow” for agiven velocity, and calculating an allowable “accumulation” in theprocessing window 1500 given a maximum “processing flow” (PRF multipliedby the link pitch).

To sever any link 1524 within the moving processing window 1500, thepositioning accuracy of the AOD 1410 shown in FIG. 14 is sufficientlysmall so as to maintain system accuracy over the entire processingwindow 1500. Present high numeric aperture lenses have a scan field ofapproximately 50 μm. Further, it may be desirable to have a system linkblow accuracy that is better than mean plus 3 sigma<0.18 μm. If, forexample, the AOD 1410 contributes approximately 20 nm of systeminaccuracy to an error budget, then the AOD 1410 according to oneembodiment has a positioning accuracy of approximately 1 part in 2500.

FIG. 17 is a schematic diagram of a laser processing system 1700comprising two deflection devices according to one embodiment. Thesystem 1700 includes the laser 1414, switch 1416, AOD 1410, relay lens1422, mirror 1424, and focus lens 1426 discussed in relation to FIG. 14.However, the system 1700 also includes another AOD 1712 and anotherrelay lens 1714 in the beam path.

In one embodiment, the AOD 1410 is configured to deflect the laser beamin the X-direction and the AOD 1712 is configured to deflect the laserbeam in the Y-direction. The relay lens 1422 images the laser beam fromthe AOD 1410 to the AOD 1712. The relay lens 1714 images the laser beamfrom the AOD 1712 to the mirror 1424. Thus, the system 1700 may redirectlaser pulses in two directions. In one embodiment, however, the AOD 1410shown in FIG. 14 comprises a single device capable of deflecting thelaser beam in two directions.

FIG. 18 is a schematic diagram of a laser processing system 1800including a telecentric angle detector 1814 according to one embodiment.In this embodiment, a partially transparent mirror 1810 directs aportion of the laser beam to the focus lens 1426 and a portion of thelaser beam to the telecentric angle detector 1814 through an additionalrelay lens 1812. The telecentric angle detector 1814 may include a quadcell, a PSD, or a camera detector configured to detect beam angle. Asdiscussed above, the telecentric angle detector 1814 may be used toprovide feedback to one or both of the AODs 1410, 1712 for errorcorrection and/or calibration.

In one embodiment, the system 1400 processes the individual links 1524in the processing window 1500 using a single pulse to blow each link1524. The AOD 1410 quickly redirects the position of the focused linkpulses to links 1524 within the processing window 1500 between twosequential laser pulses as the processing window 1500 travels in thescan direction. While a conventional link processing system may blockapproximately one-half to approximately 99% of the pulses produced by avery high PRF laser, the system 1400 may use most or all of the pulses.Thus, throughput may be greatly increased without moving the workpiece1418 faster.

In addition, or in another embodiment, the system 1400 may process asingle location on the workpiece 1418 with two or more pulses beforeusing the AOD 1410 to direct subsequent pulses to other locations on theworkpiece 1418. The system 1400 may provide ten, for example, lowerenergy pulses to a link 1524 before redirecting the laser beam to adifferent location on the workpiece 1418. Thus, the system 1400 providesan effective way of directing pulses produced at a very high PRF (e.g.,in a range between approximately 1 MHz and approximately 100 MHz) totarget desired links 1524 with many blows.

If the processing window 1500 moves continuously with respect to theworkpiece 1418, the AOD 1410 may be used to track according to oneembodiment so as to maintain a stationary relationship between a focusedspot location and a link position while one or more pulses are deliveredto the link 1524. Tracking may also be used to maintain a stationaryrelationship with a plurality of laterally spaced links.

In one embodiment, switching times between locations on the workpiece1418 are less than one laser pulse period. In another embodiment, theswitching time is on the order of the laser pulse period. In otherembodiments, the switching time is longer than the switching pulseperiod. Thus, the laser 1414 is effectively used if, for example, thesystem 1400 processes links 1524 with ten laser pulses and switches fromone link to the next in three or four laser pulse periods.

Rather than delivering all ten pulses (in the example above) to a singlelink 1522, 1524 before switching to a new location (e.g., as theprocessing window 1500 advances in the scan direction shown in FIGS. 15and 16), two or more of the pulses may be delivered to two or morelaterally spaced links 1522, 1524 (e.g., spaced perpendicular to thescan direction). For example, it may be desirable to deliver a singlepulse to each of six laterally spaced links 1522 (one in each of thelink banks 1510, 1512, 1514, 1516, 1518, 1520 shown in FIG. 15). Thus,the AOD 1410 may deflect six sequential laser pulses to the sixlaterally spaced links 1522 before shifting the processing window 1500to a new location.

FIGS. 19A, 19B and 19C are timing diagrams 1900, 1910, 1912 illustratinga series of laser pulses 1914 in relation to respective repositioningprofiles 1916, 1918, 1920 according to certain embodiments. An artisanwill understand from the disclosure herein that the timing diagrams1900, 1910, 1912 shown in FIGS. 19A, 19B and 19C are provided by way ofexample only and that any combination of pulses delivered per link andpulse periods used to shift between links may be used. In the embodimentshown in FIG. 19A, a single laser pulse is delivered to a link during ablow period. An AOD or a high speed beam deflector (not shown), forexample, is then shifted or repositioned between each pulse during ashift period. Thus, in this example, each laser pulse in the series oflaser pulses 1914 is delivered to a different link.

In the embodiment shown in FIG. 19B, the AOD or high speed beamdeflector uses more time, as compared to the example in FIG. 19A, toshift between each blow period. Specifically, after a first pulse isdelivered to a first link, the AOD or high speed beam deflector shiftsduring three pulse periods before a second pulse is delivered to asecond link. As discussed below, a switch (e.g., an additional AOD and abeam dump) may be used block the unused laser pulses from reaching thesurface of the workpiece during the shift period.

In the embodiment shown in FIG. 19C, a first plurality of pulses (nineshown) are delivered to a first link during a first blow period, the AODor high speed beam deflector shifts during a few pulse periods(approximately three shown), and a second plurality of pulses aredelivered to a second link during a second blow period. In oneembodiment, however, two or more of the first (and/or second) pluralityof pulses may distributed among a plurality of laterally spaced linksduring the first (and/or second) blow periods using a high speeddeflection device such as the AOD 1410 discussed above. Thus, pulses maybe efficiently distributed so as to utilize as many of the pulses in theseries of laser pulses 1914 as possible. In one embodiment, the numberof pulses used increases by more than approximately 1% as compared topulses utilized by conventional link processing systems.

Coherent crosstalk may be a problem for laser spots directed to processthe same target on the work surface in areas that either fully orpartially overlap, laser spots that overlap separate targets on the worksurface such that any portion of the beam (e.g., Gaussian tails)overlap, or laser spots that overlap at a detector such as a pulseenergy or reflected pulse energy detector. When Gaussian tails ofdifferent laser spots overlap, for example, crosstalk and interferencein the region between two nearby structures (e.g., links) may result indamage caused by undesirably high optical energy levels. Thus, in theembodiments discussed above, a single laser spot is incident within aprocessing window on a workpiece at a time. Two sequential laser spotsconfigured to spatially overlap on the workpiece do not interfere witheach other, thereby reducing or eliminating coherent crosstalk. However,in other embodiments, multiple spots may be incident within theprocessing window on the workpiece at the same time. For example, two ormore laser beams may be provided through two or more beam paths.

While processing a site with one or multiple blows, it is desirable touse the high speed beam steering mechanism to steer the focused spot forseveral reasons.

First, it is necessary to do beam deflection to switch between differentlink blow locations. Next, in a system in which the process area movescontinuously relative to the workpiece, it may be desirable to include atracking command. This command could help maintain a stationaryrelationship between the focused spot position and the link positionwhile one or more laser pulses are delivered to the link. A trackingcommand is particularly useful if multiple pulses are to be targeted atone link.

Additional beam deflection or steering can be used to compensate fortracking errors in motion stages. For example, if a planar XY stage isused to position the wafer under the focused laser spot, then residualXY stage tracking error (the instantaneous difference between desiredtrajectory and actual trajectory) can be compensated for using beamsteering. This is similar to our FSM error compensation.

It is also possible to use the steering mechanism to correct for othertypes of system errors or disturbances. For example, in the 9830platform we sense motion of the final focus objective and correct forthe resultant motion of the spot at the workpiece using the FSM. Thiscould be done using the same steering mechanism. We could alsocompensate for beam pointing errors, such as sensed inaccuracy in thepointing stability of the laser rail. And, other errors such as thermaldrift can be corrected using this steering mechanism.

The net tracking or steering command delivered to the AOM, EOM, or othersteering mechanism is a superposition or addition of one or more of theabove steering terms. There may also be other desirable reasons to steerbeams not noted above.

The positioning accuracy high speed beam steering device must, in oneembodiment, be small enough to maintain system accuracy over theprocessing area. Present high numeric aperture lenses have a scan fieldof approximately 50 microns, and system link blow accuracy is betterthan mean plus 3 sigma<0.18 nm. If the AOD is allowed to contribute 20nm of system inaccuracy to the error budget, then it would need theability to position with an accuracy of about 1 part in 2500. This is areasonable desire. It may be desirable to drive the AOM or high speedbeam steering device with some closed-loop sensing and feedbackcorrection.

One way to do this would be to use the AOD to deflect unwanted pulses toa beam dump that includes a position sensitive detector or quad cellthat can measure the position of these unused pulses. Thermal drifts orchanges in AOM calibration can be detected by this technique.

It may also be possible to shoot additional beams through the AOM andmeasure how they are deflected. For example, in addition to the cuttinglaser, a helium neon CW laser could be directed through the AOM and someof the resulting deflected CW beam could be directed at a PSD or quadcell for feedback purposes or for detecting drift.

It will be understood by those having skill in the art that many changesmay be made to the details of the above-described embodiments withoutdeparting from the underlying principles of the invention. The scope ofthe present invention should, therefore, be determined only by thefollowing claims.

1. A laser processing system comprising: a beam positioning system toalign beam delivery coordinates relative to a workpiece, the beampositioning system generating position data corresponding to thealignment; a pulsed laser source; a beamlet generation module to receivea laser pulse from the pulsed laser source, and to generate from thelaser pulse a beamlet array comprising a plurality of beamlet pulses; abeamlet modulator to modulate the amplitude of each beamlet pulse in thebeamlet array; and beamlet delivery optics to focus the modulatedbeamlet array onto one or more targets at locations on the workpiececorresponding to the position data.
 2. The system of claim 1, furthercomprising a photodetection module to: sample the beamlet pulses in thebeamlet array; and determine a total energy for each beamlet pulse inthe beamlet array.
 3. The system of claim 2, wherein the photodetectionmodule is further configured to provide an error correction compensationsignal to the beamlet modulator to adjust successive beamlet amplitudesprovided to a particular target on the workpiece.
 4. The system of claim2, wherein the photodetection module is further configured to: determinethat a sum of the pulse energies provided by a series of beamlet pulsesdelivered to a particular target on the workpiece meets or exceeds apredetermined threshold, and control the beamlet modulator to preventfurther beamlet pulses from reaching the particular target.
 5. Thesystem of claim 1, further comprising a system control computer tocooperate with the beam positioning system to provide the alignment bymatching a workpiece target pitch with: a pulse repetition frequency(PRF) of the pulsed laser source, a beamlet array pitch, and a relativevelocity between the beam positioning system and the workpiece (stagevelocity).
 6. The system of claim 5, wherein the beamlet pitch isrelated to the workpiece target pitch and the PRF of the pulsed lasersource through the relationship:c×(beamlet pitch)=d×(workpiece target pitch), wherein c and d areintegers, wherein:workpiece pitch=stage velocity/PRF, and wherein the integers c and d areselected such that:c/d=an integer value.
 7. The system of claim 1, wherein the beamletgeneration module comprises a discretely banded reflectivity platecomprising: a first surface comprising a first plurality of respectivelyreflective bands; and a second surface comprising a second plurality ofrespectively reflective bands; wherein the first surface is configuredto: receive the laser pulse into the discretely banded reflectivityplate; and successively reflect diminishing portions of the laser pulsereceived from the second surface back into the discretely bandedreflectivity plate toward the second surface; and wherein the secondsurface is configured to: successively transmit a first part and reflecta second part of the diminishing portions of the laser pulse receivedfrom the first surface, the transmitted first part corresponding torespective beamlet pulses in the beamlet array.
 8. The system of claim1, wherein the beamlet generation module comprises: a first quarter waveplate to receive the laser pulse, and to convert the laser pulse from alinear polarization to a circular polarization; a polarizingbeamsplitter cube comprising a first channel, a second channel, and anoutput surface, the polarizing beamsplitter cube configured to transmita first portion of the circularly polarized laser beam through theoutput surface as a first beamlet pulse in the beamlet array, and totransmit a second portion of the circularly polarized laser beam intothe first channel; a second quarter wave plate to transmit the secondportion of the circularly polarized laser beam to a first mirror, and toreceive a reflection from the first mirror to thereby convert thereflection from the first mirror into a p-polarized beam passed back tothe polarizing beamsplitter cube, wherein the polarizing beamsplittercube transmits the p-polarized beam through the second channel; and athird quarter wave plate to transmit the p-polarized beam to a secondmirror, to receive a reflection from the second mirror, and to transmitthe reflection from the second mirror back to the polarizingbeamsplitter cube, wherein the polarizing beamsplitter cube transmitsthe beam received from the third quarter wave plate through the outputsurface as a second beamlet pulse in the beamlet array.
 9. The system ofclaim 1, wherein the beamlet generation module comprises at least onediffractive optical element.
 10. The system of claim 1, wherein thepulsed laser source comprises: a photonic oscillator to emit laserpulses at a first pulse repetition frequency, the first pulse repetitionfrequency providing a reference timing signal for coordination of thebeam positioning system for the alignment of the beam deliverycoordinates relative to the workpiece; and a first optical modulator toselect, at a second pulse repetition frequency that is lower than thefirst pulse repetition frequency, a subset of the laser pulses foramplification, wherein the selection of the laser pulses included in thesubset is based on the first pulse repetition frequency and the positiondata.
 11. The system of claim 10, further comprising a laser combindexing module to adjust the alignment of the beam delivery coordinatesbased on the position data, the laser comb indexing module configuredto: select the second pulse repetition frequency such that the firstpulse repetition frequency is an integer multiple n of the second pulserepetition frequency; and offset an interpulse time between a firstamplified pulse in the subset and a second amplified pulse in the subsetby an integer multiple k of the photonic oscillator interpulse timebased on the amount of beam delivery coordinate adjustment.
 12. Thesystem of claim 1, wherein the pulsed laser source comprises a tandemphotonic amplifier including a fiber master oscillator.
 13. The systemof claim 12, wherein the fiber master oscillator is configured to outputa laser pulse with a pulse duration in a range between approximately 100femtoseconds and approximately 500 picoseconds.
 14. The system of claim1, wherein the pulsed laser source comprises a q-switched diode-pumpedsolid state laser.
 15. The system of claim 1, wherein the pulsed lasersource comprises a master oscillator power amplifier (MOPA).
 16. Thesystem of claim 15, further comprising a programmable pulsewidth elementintegrated with a master oscillator of the MOPA.
 17. The system of claim16, wherein the programmable pulsewidth element comprises a programmablebandpass filter.
 18. The system of claim 1, wherein the pulsed lasersource comprises a master oscillator regenerative amplifier.
 19. Amethod for processing a workpiece with a laser, the method comprising:generating a laser pulse; generating, from the laser pulse, a beamletarray comprising a plurality of beamlet pulses; modulating the amplitudeof each beamlet pulse in the beamlet array; and focusing the modulatedbeamlet array onto one or more target locations on the workpiece. 20.The method of claim 19, further comprising: sampling the beamlet pulsesin the beamlet array; determining a total energy for each beamlet pulsein the beamlet array; and generating an error compensation signal toadjust successive beamlet amplitudes provided to a particular target onthe workpiece.
 21. The method of claim 19, further comprising:determining that a sum of the pulse energies provided by a series ofbeamlet pulses delivered to a particular target on the workpiece meetsor exceeds a predetermined threshold, and based on the determination,preventing further beamlet pulses from reaching the particular target.22. The method of claim 19, matching a workpiece target pitch with: apulse repetition frequency (PRF) of a pulsed laser source, a beamletarray pitch, and a relative velocity between a beam positioning systemand the workpiece.